In the papermaking art, an aqueous suspension containing cellulosic fibers, and optional filler and additives, is fed into a headbox which ejects the cellulosic suspension onto a forming wire. Water is drained from the cellulosic suspension to provide a wet paper web which is further dewatered and dried in the drying section of the paper machine. Drainage and retention aids are conventionally introduced in the cellulosic suspension to facilitate drainage and increase adsorption of fine particles onto the cellulosic fibers so that they are retained with the fibers.
Silica sols are widely used as drainage and retention aids, usually in combination with charged organic polymers. Such additive systems are among the most efficient now in use in the papermaking industry. Examples of silica sols known in the art include those disclosed in U.S. Pat. Nos. 4,388,150 and 6,372,806 as well as International Patent Appl'n Publ. Nos. WO 91/07350, 91/07351, 94/05596, 98/30753, 98/56715, 00/66491, 00/66492, 2005/097678, 2005/100241, 2008/150230 and 2010/006994.
It would be desirable to provide a silica sol with improved drainage and retention performance in the production of paper and board. It would also be desirable to provide a method for producing such a silica sol. It would also be desirable to provide a process for making paper and board with improved drainage and retention performance.